Various approaches can be used for detecting exhaust pressure buildup in an engine exhaust system, such as exhaust pressure sensors measuring pressure differential across an emission control device.
However, the inventors herein have recognized that such an approach may require additional sensors that can add to system cost.
Further, the inventors herein have recognized that it may be possible to provide the desired detection using already available information, such as information from an exhaust gas recirculation system.
In one example, advantages over prior approaches are provided by a method for detecting pressure buildup in an exhaust passage of an internal combustion engine having an emission control device and an exhaust gas recirculation system with an exhaust valve. The method comprises:                moving the exhaust valve in the exhaust gas recirculation system to a preselected open position; and        estimating exhaust pressure buildup based on manifold pressure and an indication of pressure in the exhaust gas recirculation system.        
In another aspect, it includes a method for detecting pressure buildup in an exhaust passage of an internal combustion engine having an emission control device and an exhaust gas recirculation system with an exhaust valve and a sensor, comprising:                detecting exhaust pressure buildup based information from the senor in the exhaust gas recirculation system.        
By utilizing an exhaust gas recirculation system, it may be possible to provide the desired diagnostics with sufficient accuracy, without requiring additional exhaust gas sensors. Although, in one example the approach herein can be used in addition to other sensors to increase detection accuracy.
An advantage of the invention is improved degradation detection.